Processing of soap



Sept. 1, 1959 1.. D. JONES 2,902,502

PROCESSING OF SOAP Filed May 10, 1957 Water and/or 23 Electrolyte 8 centrifuge R Nigre 22 2| *5 i; /9 l3 I? I8 7 i Gruined Soap L Nee Soap Mass NW8 6 Mixer 7 (@zzlz-rw IH\ L);

INVENTOR. LEO D. JONES BY/Ag/ GM AT TQRNEY ed States, Patent Qfiice 2,902,502 Patented Sept. 1, 1959 PROCESSING OF SOAP Leo D. Jones, Philadelphia, Pa., assignor to The Sharples Corporation, a corporation of Delaware Application May 10, 1957, Serial No. 658,452 11 Claims. (Cl. 260-418) This invention pertains generally to the manufacture of soap, and particularly to the manufacture of neat soap from vegetable and animal oils and fats.

The term neat soap is used herein in its original sense, that is as it is applied by the practical soap-maker, namely, to designate a type of soap which results from an operation known in the art as fitting and settling, wherein soap originally in grained condition is partially dissolved by the addition of water with or without electrolyte to produce an aqueous soap solution called nigre, and separating the undissolved soap from the nigre. The soap after separation from the nigre is in the condition called neat soap.

The invention will be described more particularly in connection with the continuous fitting of grained soap (also called washed soap or curd soap) having a total fatty acid content (TFA) of at least 60%, such as from 60 to 65%, as to which it is outstandingly useful, but it is to be understood that some of the advantages of the invention accrue even when it is applied to the fitting of soap originally of lower TFA.

Grained soaps having total fatty acid contents of from 60 to 65% are readily obtainable in continuous processes for the manufacture of soap wherein centrifuges are employed for the separation from the soap of the aqueous electrolyte solution, usually called lye, employed for graining (washing) purposes. Grained soaps having total fatty acid contents below 60% are largely produced in batch operations conducted in kettles, or in continuous processes wherein separation of the soap from the lye is effected by gravity settling.

In the manufacture of soap, the purposes, functions and operations of what is generally called graining are Well known, and do not require further description. In such operations, the electrolyte content of the lye, which customarily is sodium chloride (herein referred to as salt) and/or sodium hydroxide, may be varied as desired to produce what is known as a soft grain, or a hard grain, or a grain in between, though it is generally recognized that in most instances it is preferable to operate with the electrolyte content in the lye approximately just sufficiently high to avoid significant solution of soap in the lye.

While saponification operations have been carried out ;-with a variety of alkalies, the one most commonly employed for the production of soluble soap is sodium hydroxide, and it is to the processing of sodium soap that this invention particularly relates. 1

While sodium soap in grained condition, and especially when the grain is relatively soft, can be manufactured directly into bars without resorting to the step of fitting, provided that the TFA is sufficiently high, there is nevertheless still a large demand for bar soap made from neat soap, because the latter soap is somewhat smoother in appearance, and has a somewhat lesser tendency to fracture.

In fitting operations as normally carried out, a considerable percentage of the soap in process is dissolved to form the nigre which must be reprocessed to recover its soap values at the cost of both time and expense. The capacity of a plant is reduced by the percentage of nigre which must be reprocessed, and the step of reprocessing nigre adds to the expense of operations.

When separations of the lye from the grained soap prior to fitting are carried out by gravity settling, and particularly when the operations are carried out in kettles, removal of impurities including color bodies from the soap is not accomplished efficiently, with the result that the nigre formed in the fitting step carries with it a considerable amount of impurities washed from the soap including color bodies, and such nigre usually is employed in the production of lower grade soap. Grained soap produced continuously in processes involving the centrifugal separation of the lye from the soap, on the other hand, is usually so free from impurities just prior to fitting, that the nigre produced during fitting is in substantially the same state of purity as the main body of soap.

An outstanding feature of this invention resides in the continuous production of neat soap from grained soap without taking into solution a large percentage of the grained soap as is done in normal fitting operations.

By the use of this invention the capacity of a plant of a given size is markedly increased, and substantial savings, both in time and expense are made, due to the avoidance of reprocessing large quantities of soap in the form of nigre.

' A further feature of the invention resides in the simplification of the fitting operation.

A further feature resides in the fact that close control of the fitting operation is afforded.

Further features of the invention will become apparent to persons skilled in the art as the specification proceeds, and upon reference to the drawings in which:

The single figure is a flow sheet illustrating apparatus for the practice of the invention.

Referring now to the drawings, a circulatory system is illustrated diagrammatically as comprising mixer 1, conduit 2, pump 3, conduit 4, valve 5, conduit 6, centrifuge 7, conduit 8, overflow container 9, conduit 10, and level control valve 11.

'= pump 3, this nigre is circulated from mixer 1 through conduit 2, pump 3, conduit 4, valve 5, conduit 6 to the centrifuge 7. With only nigre present in the flowing stream, all of the material fed to the centrifuge 7 is made to discharge therefrom through conduit 3 into overflow tank 9. As shown, conduit 10 extends up into tank 9 a substantial distance with its upper end 15 stopping short of the top of the tank, for purposes to be hereinafter described. When the level of nigre in tank 9 reaches top 15 of conduit 10, nigre flows into conduit 10, and is re turned to mixer 1 through level control valve 11. Mixer 1 may be of any desired type. As illustrated it contains a motor driven agitator 12.

In accordance with the invention, a grained soap mass, preferably separated centrifugally from an aqueous electrolyte washing, i.e. graining solution, e.g. from a continuous soap manufacturing process such as the grained soap discharged from centrifuge 24 of U8. Patent 2,300,750, or the grained soap discharged from centrifuge 27 of US. Patent 2,300,749, is delivered continuously through conduit 13 into mixer 1.

In mixer 1 the grained soap reacts physically with the nigre, and is converted into neat soap.

A continuous stream of the mixture of neat soap and nigre flows to centrifuge 7 where the two are continuously separated. Nigre is discharged through conduit 8 and is delivered to container 9, as previously described, and

neat soap is discharged through conduit 14, and delivered to any suitable point, not shown.

Since with grained soap of high TFA there is substantially no, or at most very little, change in the composition of the grained soap mass in its conversion into neat soap, and substantially no, or at most very little, change in the composition of the nigre, the ratio of neat soap to nigre in the mixer 1 remains substantially the same as the ratio between the rate of flow of grained soap mass through conduit 13 and the rate of flow of nigre through conduit 10 into the mixer 1. It is a mixture of neat soap and nigre in substantially this ratio that passes from the mixer 1, through the pump 3, through the valve 5, to centrifuge 7. Increasing the total rate of flow of the mixture passing from mixer 1 through pump 3 and valve 5 into centrifuge 7, as by increasing the pumping effect of the pump 3 and/ or by increasing the opening of valve 5, the rate of feed of grained soap mass to mixer 1 through conduit 13 remaining constant, increases the rate of discharge of nigre from the centrifuge '7 and the rate of return of nigre to mixer 1. Since the rate of return of nigre to mixer 1 has increased with respect to the rate of feed of grained soap mass to the mixer 1 (which has remained constant), the ratio of neat soap to nigre in the mixer 1 is gradually reduced and accordingly the ratio of neat soap in the feed to the centrifuge 7 is reduced. Decreasing the total rate of flow of the mixture passing from mixer 1 to centrifuge 7, on the other hand, causes the ratio of neat soap to nigre in the mixer 1 to be increased. Thus by the control of pump 3 and/or the valve 5, any desired ratio of nigre to neat soap in the mixer 1 may be maintained.

It is preferable to maintain a ratio of nigre to neat soap within the range normally used in conventional kettle fitting, although any other ratio may be employed. Thus, for example, the ratio may be 5 to 35% nigre to 95 to 65% neat soap. A ratio of 20 to 30% nigre to 80 to 70% neat soap is particularly satisfactory.

An outstanding feature of this invention resides in the fact that both the composition and the quality of the neat soap separated and discharged from centrifuge 7 through conduit 14, are relatively independent of the ratio of nigre to neat soap maintained in the mixer 1, and in the stream of the mixture thereof flowing to centrifuge 7, and, therefore, both are relatively independent of the rate at which the grained soap mass is fed into mixer 1 through conduit 13.

The term nigre is used herein to mean an aqueous solution of soap also containing in solution electrolyte such as sodium chloride and/or sodium hydroxide. The concentration of soap in solution may vary from a total fatty acid content of say 1% to a total fatty acid content of say 40%, although lower and higher percentages are possible depending, of course, on the amount of electrolyte in solution and the composition of the soap. A nigre is usually considered to be a saturated solution of soap with the amount of soap in solution governed by the percentage of electrolyte present. While the present invention contemplates the use of nigre of any total fatty acid content, it is preferred to employ nigre having total fatty acid contents between 2 and 30%, and particularly between 5 and 15%.

While the process may be operated under any desired temperature conditions, it is preferred to operate between 170 F. and 215 F. in the various parts of the system, the lower temperatures usually being employed when processing the more soluble soaps, and the higher temperatures when processing the less soluble soaps. Any suitable temperature control means may be employed such as a heat exchange unit 31 shown in mixer 1 for heating or cooling as desired.

While it has not been definitely established, it appears that the dispersed soap particles, that is soap hydrate apart from entrained aqueous solution, in both a grained soap mass and in neat soap are of substantially the same 1 chemical composition and physical nature, but that in a grained soap mass these particles are surrounded with an aqueous solution of caustic soda and/or salt which does not dissolve soap, and which only imperfectly wets the surfaces of the particles, whereas in neat soap the particles are surrounded with an aqueous solution of soap called nigre which wets the particles, with the result that the neat soap is considerably more homogeneous than the grained soap mass. It is apparently by the Wetting of the particles in the grained soap mass with nigre in accordance with this invention that the grained soap mass is converted into neat soap.

When the grained soap mass enters the mixer 1 and comes into intimate contact with the nigre contained therein, it appears that the particles in the grained soap mass are quickly surrounded and wetted by nigre, aqueous graining electrolyte intermixed with the particles becoming embodied in the nigre by solution therein, the result of which is that the grained soap mass is converted into neat soap.

In the practice of this invention, the neat soap discharged from the centrifuge 7 through conduit 14 may have a slightly different overall composition than that of the grained soap mass entering through the conduit 13. The grained soap mass may, for instance, have a total fatty acid content of 63%, a caustic soda content of 0.35%, and a salt content of 0.35%. When a grained soap mass of this character is treated in accordance with this invention, a typical composition of the resulting neat soap mass discharging from conduit 14 is as follows; total fatty acids 63%, caustic soda 0.20%, and salt 0.20%. The differences between these two compositions, namely, 0.15% of caustic soda and 0.15% of salt are dissolved in the nigre, with an increase in the content of these electrolytes in the nigre.

To avoid the building up of electrolyte, e.g. caustic soda and/ or salt, in the nigre, Water may be fed to mixer 1 through conduit 17 at a rate having a desired relation to the rate at which grained soap mass is fed through conduit 13 into mixer 1, to maintain the concentration of electrolyte in the nigre in the circulating system relatively uniform and at the chosen level. The amount of water required for this purpose is surprisingly small. For instance, in the example mentioned above, the addition of approximately 3.6 parts by weight of water for each parts of grained soap mass fed to the mixer 1 through conduit 13 maintains the nigre in the circulating system at a concentration which continuously yields neat soap at the centrifuge 7.

In the above example, the water to be added to the continuous system was determined by comparing the caustic soda and/ or salt content of the grained soap mass with that of the neat soap. A somewhat preferred method of operation, however, is to determine from time to time the caustic soda content of the nigre flowing through conduit 10 by simple laboratory titration. The fiow of water through conduit 17 is then controlled by valve 21 to maintain the caustic soda content of the nigre flowing through conduit 10 substantially constant. The addition of water does not affect the ratio of salt (sodium chloride) to caustic soda. Therefore, by maintaining the caustic soda content constant, the salt content likewise is maintained constant. As a result a uniform quality oft s neat soap is discharged from the centrifuge through conduit 14.

Additional nigre is formed as a result of the addition of water to mixer 1, but, in normal operation with grained soap masses above 60% TFA, this is small, e.g. less than 1% of the anhydrous soap content of the grained soap mass entering the mixer 1. In the conventional process of fitting, at least 10% of the soap in the grained soap mass is converted into nigre which upon separation must be reworked.

In accordance with the embodiment of my invention particularly described, the nigre discharged from the centrifuge 7 flows through conduit 8 into overflow tank 9, and then through conduit 10 and constant level valve 11 into the mixer 1. In this embodiment, the mixer 1 is maintained full of liquid up to the level controlled by the constant level valve 11. The overflow container 9 also is maintained full of liquid up to above the top 15 of conduit 10. An appropriate level for the latter purpose is maintained in container 9 by the S-shaped overflow conduit 18, the lower end of which connects with the bottom of container 9, and the upper end of which is so arranged that its outlet is higher than top 15 of conduit 10 This arrangement maintains a constant volume of nigre circulating in the systemillustrated in Figure 1 when the feed of grained soap mass to mixer 1 is maintained constant, and is adapted to automatically adjust to variations in the ratio of soap to nigre. Moreover, as and if additional nigre is formed, as by the addition of water from conduit 17, any excess overflows through conduit 18, and preferably is returned to some suitable point for recovery of its soap values.

It is known to those skilled in the art of soap manufacture that when a grained soap mass is fitted for separation of a neat soap from nigre, there may occur, in addition to nigre, a separate aqueous solution of electrolyte, e.g. of caustic soda and/or salt, which contains substantially no soap dissolved in it, and which is mutually insoluble with the soap particles of the neat soap and the nigre. This aqueous solution is commonly referred to as pitch water.

It-is entirely within the purview of this invention for there to exist within the circulating system thereof not only nigre, but also pitch water. When pitch water is present, it is preferably made to discharge from the centrifuge 7 through conduit 8 along with the nigre into overflow container 9, and removed in whole or in part from the system, for example, as follows. Pitch water is heavier than nigre, and separates readilytherefrom by gravity. In the overflow container 9 the nigre and the pitch water separate by gravity. Overflow conduit 18 is connected to the bottom of overflow container 9, and since pitch water is the lower layer, it overflows from container 9 in preference to nigre, and is thus removed from the system. Whether it is pitch water or nigre, any (Excess in the circulating system overflows through conuit 18.

In the above example, caustic soda and salt (sodium chloride) are present in relatively equal amounts in the grained soap mass, and in relatively equal amounts in the neat soap. Other ratios of these two graining agents or electrolytes with respect to each other are frequently desired in the neat soap depending upon the ultimate product manufactured from the neat soap. It is preferred to control the ratio of caustic soda to salt in the neat soap by controlling the ratio of caustic soda to salt in the graining operation by which the grained soap mass is prepared so that nothing, or at least only water, need to be added for the conversion of the grained soap mass to the desired neat soap in the practice of the invention. It is, however, within the purview of this invention to add electrolyte (e.g. caustic soda, and/or salt) and/or water to the mixer 1 to modify or adjust the ratio of caustic soda to salt in the neat soap. It will be understood that either electrolyte may be substantially zero in the grained soap and/or finally separated neat soap.

It is particularly advantageous in the practice of this invention to charge to mixer 1 through line 13 a grained soap mass which has been grained or washed with an aqueous solution of electrolyte, i.e. lye, containing a percentage of electrolyte just sufliciently high (or only slightly higher, e.g. by 1%) to prevent significant solution of soap in the lye. The residual or entrained lye in the grained soap mass will, of course, be of the same electrolyte concentration.

All percentages referred to herein are by weight unless otherwise noted. In the centrifuge 7, when separating neat soap from nigre and/or pitch water, the control of the separation may be by any desired means known in the art without departing from the spirit of my invention. One method of control particularly adapted to open bowl type centrifuges employs balanced layers within the centrifugal bowl or rotor. Another method of control particularly adapted to full bowl type centrifuges employs valves for restricting the flow of one or both of the separately discharging streams, as by way of example valve 22 in conduit 14 and/or valve 23 in conduit 8.

Difiiculty is sometimes experienced in controlling the respective discharges of neat soap and nigre from a centrifuge bowl, because of their similarity in appearance and their relatively close specific gravities. Neat soap is the final product, and preferably, when such dilficulty arises, the control of the centrifuge is such that a small amount of neat soap is discharged along with the nigre and/or pitch water to insure the discharge of neat soap uncontaminated with nigre and/ or pitch water that should have been discharged with the main body thereof. Any neat soap so discharged through conduit 8 from the centrifuge 7 is recovered as the nigre (and pitch water if present) is circulated from mixer 1 through the centrifuge 7.

It is to be understood that the above particular description is by way of illustration and that changes, omissions, additions, substitutions and/or modifications may be made within the scope of the appended claims without departing from the spirit thereof.

For instance, while I have referred to one method'of obtaining grained soap of at least 60% total fatty acid content, namely, by separating the lye from the grained soap by the use of a centrifuge in a continuous process for the manufacture of soap, any other method of accomplishing the same result may be employed. For example/the literature refers to rare instances in which grained soap of 60% TFA has been obtained by gravity settling in kettle practice. Also, after graining soap in a kettle, the mass might be fed to a centrifuge for the separation of the lye from the soap to obtain a grained soap of relatively high T FA.

It is recognized that kettle-made soaps carry substantially more color bodies into the fitting stage than continuously-made soaps from processes wherein the lye is separated from the grained soap by the use of centrifuges. While grained soap made in etlicient continuous centriugal processes is relatively free from color bodies insoluble in lye but soluble in nigre, on occasion such color bodies might be present to an indesirable extent in the grained soap feed. To avoid the building up of such color bodies in the nigre in such situations, any of several expedients may be resorted to. One such expedient is to feed water into mixer 1 through line 17, or if water is already being fed, then to increase the feed of such water, if desirable, so as to provide for the continuous production of fresh nigre from the grained soap feed in desired or suitable amount, and for the continuous discharge of a stream, usually small, of nigre from overflow conduit 18 to carry off color bodies in nigre thus discharged, and thus prevent color in the nigre in the process from exceeding a chosen upper level. In fact, since even in normal operation it is customary to continuously feed a small stream of water at 17 into mixer 1, even when operating with a feed of centrifugally separated grained soap, this precaution against the buildup of color bodies in the nigre to an undesirably high level is usually present in ordinary operation, whether necessary or not. In any case, electrolyte may be fed into mixer 1 along with the water necessary or desirable in order to control the amount of soap dissolved by the addition of the water and/or to control the electrolyte concentration in the nigre.

n the other hand, any means for purifying nigre may be employed, say between the discharge of nigre from centrifuge 7 and the feed of nigre back into mixer 1. Various methods for the purification of nigre are described in the literature.

Other variations are possible.

Accordingly it is intended that the patent shall cover by suitable expression in the claims the various features of patentable novelty that reside in the invention.

I claim:

1. A process for converting grained soap into neat soap which comprises bringing an aqueous solution of soap into contact with and mixing it with grained soap in the presence of an electrolyte limiting the solubility of soap in said solution to form. a mixture of neat soap and an electrolyte-containing aqueous soltuion of soap, and separating said neat soap from said aqueous solution.

2. A process for converting grained soap into neat soap which comprises mixing a stream of said grained soap with a stream of an aqueous solution of soap in the presence of an electrolyte limiting the solubility of soap in said solution to form a mixture of neat soap and an electrolyte-containing aqueous solution of soap, separating a stream of said mixture into neat soap and an electrolyte-containing aqueous solution of soap, and recycling said separated aqueous solution to the source of said firstmentioned aqueous solution of scap.

3. The process of claim 2 wherein the soap is sodium soap, and the electrolyte is comprised of at least one of a group consisting of sodium chloride and sodium hydroxide.

4. A process for converting grained soap contained in a grained soap mass into neat soap, said grained soap mass having a total fatty acid content of at least 60%, which comprises feeding a stream of said grained soap mass to a zone of mixing and mixing it therein with a stream of an electrolyte-containing aqueous solution of soap to form a mixture of neat soap and an electrolytecontaining aqueous solution of soap to form a mixture of neat soap and an electrolyte-containing aqueous solution of soap; conducting a stream of said mixture to a'zone of centrifugation and therein separating said last-mentioned stream into heat soap and an eletcrolyte-containing aqueous solution of soap, and recycling said separated electrolyte-containing aqueous solution of' soap to the source of said first-mentioned electrolyte-containing aqueous solution of soap.

5. The process of claim 4 wherein water is added to control the electrolyte concentration inthe electrolytecontaining aqueous solution of soap. 1

6. The process of claim 5 wherein electrolyte is added in addition to water. Y

7. The process ofclaim 5 wherein a part of the elec trolyte-containing aqueous solution of soap is withdrawn from the process.

8. The process of claim 4 wherein the total fatty acid content of the aqueous solution of soap charged to the mixing zone is maintained between 1% and 40%.

9. The process of claim 8 wherein the total fatty acid content is maintained between 2% and 30%.

10. The process of claim 9 wherein the total fatty acid content is maintained between 5% and 11. The process of claim 4 wherein the grained soap mass contains residual lye which is of an electrolyte content above and close to that concentration below which soap would dissolve therein to a significant extent.

Scott et al. Nov. 3, 1942 Scott et al. Nov. 3; 1942.

OTHER REFERENCES The Sharples Corp. Bulletin 1241, entitled, The Sharples Centrifugal Soap Process, received in Division Sept. 22, 1948. 

